SapienzaExamHandler#_insertReservation broken

[matypist]

{"esito":{"flagEsito":-1,"id":0,"nota":"Selezionare una modalità di prenotazione.","ritorno":null},"output":null,"url":null,"urlOpis":null}

Some screenshots from the website:

(When trying to book the exam without having the required option selected)

See also leosarra/openstud_client#31